Microsoft stated that this is due to changes made by Facebook to their Graph API, "the tool that we use to connect your Microsoft account to Facebook. It brings contact information from your Facebook friends into Outlook.com and the Windows People app, keeps those contacts up-to-date, and provides options in apps and services like Photo Gallery, Movie Maker, and OneDrive.com to share to Facebook. We collectively refer to these features as Facebook Connect."

What users will lose

Impact on Outlook.com contacts: New users may lose out on integrating Facebook contacts to their Outlook.com accounts and existing users will not be able to update Facebook contacts to their email.

Impact on OneDrive online service: Users would no longer have the publish to sidebar link feature.

Impact on Office 365 Outlook Web App: In Office 365, the entire Facebook Connect package will not be available if users have connected to Facebook via Outlook Web application. User's Facebook contacts will also not automatically synchronise to their Office 365 account. Moreover, new Outlook 365 users will not be able to connect to Facebook via the Outlook Web application.

Impact on Windows Live Essentials Calendar and Contacts: Users will not receive event/contact updates from Facebook.